The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

https://www.ch.ic.ac.uk/local/organic/pericyclic/DA.pdf

The Diels--Alder reaction in total synthesis.

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Publisher Summary This chapter discusses prostaglandins and thromboxanes. The prostaglandins are C 20 acids formed from polyunsaturated fatty acids by oxygenation and cyclization. The thromboxanes, which were originally found in platelets, have now been identified in a variety of tissues. Rapid progress is being made in understanding their biological roles. Earlier studies on vascular and airway smooth muscle demonstrated that endoperoxides had unique effects that could not be attributed to conversion into the stable prostaglandins. Because aspirin, an inhibitor of endoperoxide formation, inhibits the second wave of aggregation, it was suggested that the endoperoxides play a role in the release reaction. The potency of the endoperoxides in causing contractions of the isolated rabbit aorta was of particular interest. However, the occurrence of thromboxanes is not limited to platelets. The transformation of arachidonic acid into thromboxane B 2 has also been observed in lung tissue, spleen, kidney, leukocytes, umbilical artery, and brain.

Prostaglandins and thromboxanes.

One hundred years after the birth of Kurt Alder and seventy-five years after the discovery of his famous reaction, one of the most important and fascinating transformations in chemistry, research on that process continues to surprise, excite, delight, and inform the chemical community. This article is based on presentations given first at the University of Cologne, Germany (Kurt Alder lecture, 1992), then at the Roger Adams Award Symposium (1993), and later at the Burgenstock Conference of 2001, and describes research by our group on the development and understanding of enantioselective versions of the Diels-Alder reactions. The elements of this review include (1) development of new chiral Lewis acid catalysts for highly enantioselective (>25:1) [4+2] cycloadditions; (2) the fine mechanistic details and pre-transition-state assemblies of these reactions; (3) the fundamental understanding of catalytic activity and enantioselectivity for highly enantioselective Diels-Alder processes; and (4) applications to the synthesis of complex molecules. The range and power of the Diels-Alder reaction have steadily increased over seven decades. The end of this remarkable development is not in sight, a high compliment to this field of Science and to its great inventor.

Catalytic enantioselective Diels--Alder reactions: methods, mechanistic fundamentals, pathways, and applications.

Enzymes as catalysts in synthetic organic chemistry gained importance in the latter half of the 20th century, but nevertheless suffered from two major limitations. First, many enzymes were not accessible in large enough quantities for practical applications. The advent of recombinant DNA technology changed this dramatically in the late 1970s. Second, many enzymes showed a narrow substrate scope, often poor stereo- and/or regioselectivity and/or insufficient stability under operating conditions. With the development of directed evolution beginning in the 1990s and continuing to the present day, all of these problems can be addressed and generally solved. The present Perspective focuses on these and other developments which have popularized enzymes as part of the toolkit of synthetic organic chemists and biotechnologists. Included is a discussion of the scope and limitation of cascade reactions using enzyme mixtures in vitro and of metabolic engineering of pathways in cells as factories for the production o...

Robert B. Woodward

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